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Abstract:

This document discloses a solution for transmitting scanning response
messages in an orderly manner in a wireless network. An access node
determines a transmission order for a plurality of access nodes
responding to a scanning request message provided by a
scanning/requesting device. Then, the access node determines its own
transmission turn within the transmission order and transmits a scanning
response message with reduced channel contention. Another aspect relates
to the scanning device arranged to receive the scanning response messages
where the scanning device monitors the transmission order of the scanning
response messages.

Claims:

1. A method comprising: acquiring, in an access node of a wireless
network, neighbour access node information comprising at least one of
identification, geographical location, and characteristics of at least
one neighbouring access node; acquiring a scanning request message
originated from a requesting device; determining, at least partly on the
basis of the neighbour access node information, a transmission order of a
plurality of scanning responses that respond to the scanning request; and
causing the access node to transmit a scanning response during a
transmission turn of the access node determined from the transmission
order.

2. The method of claim 1, wherein the identification comprises a medium
access control address of the at least one neighbouring access node, and
wherein the transmission order is determined from the medium access
control address values of the access node and the at least one
neighbouring access node by sorting the medium access control address
values into an ascending or descending order.

3. The method of claim 1, wherein the scanning request comprises context
information, the method further comprising determining the transmission
order of the plurality of the scanning responses further on the basis of
the context information of the scanning request.

4. The method of claim 3, wherein the context information comprises at
least one of a location of the requesting device, a distance parameter
defining a response zone in which the scanning response is requested, a
service requirement of the requesting device, and a maximum number of
responses requested by the requesting device.

5. The method of claim 1, wherein if the transmission turn of the access
node is the first transmission turn in the transmission order, causing
the access node to transmit the scanning response message on a channel
upon detecting that the channel has been free for a first duration, and
if the transmission turn of the access node is later than the first
transmission turn in the transmission order, causing the access node to
transmit the scanning response message during its transmission turn on
the channel upon detecting that the channel has been free for a second
duration which is shorter than the first duration.

6. The method of claim 1, further comprising causing the access node to
transmit a scanning response amongst the plurality of scanning responses
to the requesting device in a transmission turn of the access node
determined from the transmission order, wherein the scanning response
comprises a transmission turn indicator indicating the transmission turn
of the access node within the transmission order of the plurality of
scanning responses.

7. The method of claim 1, wherein the scanning request comprises the
location of the requesting device, the method further comprising:
acquiring locations of neighbour access nodes; and determining the
transmission order from the locations of the access node and the
neighbour access nodes.

8-11. (canceled)

12. The method of claim 1, wherein the scanning request comprises a probe
request, the scanning response comprises a probe response, and the
neighbour access node comprises a neighbour access point of an IEEE
802.11 network.

13. A method comprising: causing a scanning device to transmit a scanning
request comprising context information to a plurality of access nodes;
acquiring in the scanning device a scanning response from an access node,
wherein the scanning response comprises an information element indicating
a transmission turn of the scanning response in a transmission order of a
plurality of scanning responses responding to the scanning request.

14. The method of claim 13, wherein the context information comprises at
least one of a location of the scanning device, a distance parameter
defining a response zone in which the scanning response is requested, a
service requirement of the scanning device, and a maximum number of
responses requested by the scanning device.

15. (canceled)

16. The method of claim 13, further comprising: determining from the
transmission turn acquired from the scanning response that at least one
other scanning response having a prior transmission turn has not been
acquired; and in response to determining that the at least one other
scanning response has not been acquired, causing the scanning device to
transmit another scanning request to receive the at least one other
scanning response that was determined as not received.

17. (canceled)

18. An apparatus comprising: at least one processor; and at least one
memory comprising a computer program code, wherein the at least one
memory and the computer program code are configured, with the at least
one processor, to cause the apparatus to: acquire neighbour access node
information comprising at least one of identification, geographical
location, and characteristics of at least one neighbouring access node;
acquire a scanning request message originated from a requesting device;
determine, at least partly on the basis of the neighbour access node
information, a transmission order of a plurality of scanning responses
that respond to the scanning request; and cause an access node to
transmit a scanning response during a transmission turn of the access
node determined from the transmission order.

19. The apparatus of claim 18, wherein the identification comprises a
medium access control address of the at least one neighbouring access
node, and wherein the at least one memory and the computer program code
are configured, with the at least one processor, to cause the apparatus
to determine the transmission order from the medium access control
address values of the access node and the at least one neighbouring
access node by sorting the medium access control address values into an
ascending or descending order.

20. The apparatus of claim 18, wherein the scanning request comprises
context information, and wherein the at least one memory and the computer
program code are configured, with the at least one processor, to cause
the apparatus to determine the transmission order of the plurality of the
scanning responses further on the basis of the context information of the
scanning request.

21. The apparatus of claim 20, wherein the context information comprises
at least one of a location of the requesting device, a distance parameter
defining a response zone in which the scanning response is requested, a
service requirement of the requesting device, and a maximum number of
responses requested by the requesting device.

22. The apparatus of claim 18, wherein if the transmission turn of the
access node is the first transmission turn in the transmission order, the
at least one memory and the computer program code are configured, with
the at least one processor, to cause the apparatus to cause the access
node to transmit the scanning response message on a channel upon
detecting that the channel has been free for a first duration, and if the
transmission turn of the access node is later than the first transmission
turn in the transmission order, the at least one memory and the computer
program code are configured, with the at least one processor, to cause
the apparatus to cause the access node to transmit the scanning response
message during its transmission turn on the channel upon detecting that
the channel has been free for a second duration which is shorter than the
first duration.

23. The apparatus of claim 18, wherein the at least one memory and the
computer program code are configured, with the at least one processor, to
cause the apparatus to cause the access node to transmit a scanning
response amongst the plurality of scanning responses to the requesting
device in a transmission turn of the access node determined from the
transmission order, wherein the scanning response comprises a
transmission turn indicator indicating the transmission turn of the
access node within the transmission order of the plurality of scanning
responses.

24. The apparatus of claim 18, wherein the scanning request comprises the
location of the requesting device, and wherein the at least one memory
and the computer program code are configured, with the at least one
processor, to cause the apparatus to: acquire locations of neighbour
access nodes; and determine the transmission order from the locations of
the access node and the neighbour access nodes.

25-28. (canceled)

29. The apparatus of claim 18, wherein the scanning request comprises a
probe request, the scanning response comprises a probe response, and the
neighbour access node comprises a neighbour access point of an IEEE
802.11 network.

30. An apparatus comprising: at least one processor; and at least one
memory comprising a computer program code, wherein the at least one
memory and the computer program code are configured, with the at least
one processor, to cause the apparatus to: cause a scanning device to
transmit a scanning request comprising context information to a plurality
of access nodes; acquire a scanning response from an access node, wherein
the scanning response comprises an information element indicating a
transmission turn of the scanning response in a transmission order of a
plurality of scanning responses responding to the scanning request.

31. The apparatus of claim 30, wherein the context information comprises
at least one of a location of the scanning device, a distance parameter
defining a response zone in which the scanning response is requested, a
service requirement of the scanning device, and a maximum number of
responses requested by the scanning device.

32. (canceled)

33. The apparatus of claim 30, wherein the at least one memory and the
computer program code are configured, with the at least one processor, to
cause the apparatus to: determine from the transmission turn acquired
from the scanning response that at least one other scanning response
having a prior transmission turn has not been acquired; and in response
to determining that the at least one other scanning response has not been
acquired, cause the scanning device to transmit another scanning request
to receive the at least one other scanning response that was determined
as not received.

34-37. (canceled)

Description:

FIELD

[0001] The invention relates to the field of wireless networks and,
particularly, to processing scanning request messages and scanning
response messages in a wireless network.

BACKGROUND

[0002] Some modern wireless networks employ an active scanning procedure
in which a scanning device scans for presence of wireless networks. The
active scanning comprises transmitting a scanning request message and any
access node of a wireless network detecting the scanning request may
respond to it by transmitting a scanning response message. However, in a
case where there are several wireless networks present in the area, the
number of scanning responses may become substantially high which causes
high signalling overhead and increases channel collisions.

BRIEF DESCRIPTION

[0003] According to an aspect of the present invention, there is provided
a method comprising: acquiring, in an access node of a wireless network,
neighbour access node information comprising at least one of
identification, geographical location, and characteristics of at least
one neighbouring access node; acquiring a scanning request message
originated from a requesting device; determining, at least partly on the
basis of the neighbour access node information, a transmission order of a
plurality of scanning responses that respond to the scanning request; and
causing the access node to transmit a scanning response during a
transmission turn of the access node determined from the transmission
order.

[0004] According to another aspect of the present invention, there is
provided a method comprising: causing a scanning device to transmit a
scanning request comprising context information to a plurality of access
nodes; acquiring in the scanning device a scanning response from an
access node, wherein the scanning response comprises an information
element indicating a transmission turn of the scanning response in a
transmission order of a plurality of scanning responses responding to the
scanning request.

[0005] According to another aspect of the present invention, there is
provided an apparatus comprising at least one processor and at least one
memory comprising a computer program code. The at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to: acquire neighbour access node
information comprising at least one of identification, geographical
location, and characteristics of at least one neighbouring access node;
acquire a scanning request message originated from a requesting device;
determine, at least partly on the basis of the neighbour access node
information, a transmission order of a plurality of scanning responses
that respond to the scanning request; and cause an access node to
transmit a scanning response during a transmission turn of the access
node determined from the transmission order.

[0006] According to another aspect of the present invention, there is
provided an apparatus comprising at least one processor and at least one
memory comprising a computer program code. The at least one memory and
the computer program code are configured, with the at least one
processor, to cause the apparatus to: cause a scanning device to transmit
a scanning request comprising context information to a plurality of
access nodes; acquire a scanning response from an access node, wherein
the scanning response comprises an information element indicating a
transmission turn of the scanning response in a transmission order of a
plurality of scanning responses responding to the scanning request.

[0007] According to another aspect of the present invention, there is
provided an apparatus comprising: means for acquiring, in an access node
of a wireless network, neighbour access node information comprising at
least one of identification, geographical location, and characteristics
of at least one neighbouring access node; means for acquiring a scanning
request message originated from a requesting device; means for
determining, at least partly on the basis of the neighbour access node
information, a transmission order of a plurality of scanning responses
that respond to the scanning request; and means for causing the access
node to transmit a scanning response during a transmission turn of the
access node determined from the transmission order.

[0008] According to another aspect of the present invention, there is
provided an apparatus comprising means for causing a scanning device to
transmit a scanning request comprising context information to a plurality
of access nodes; and means for acquiring in the scanning device a
scanning response from an access node, wherein the scanning response
comprises an information element indicating a transmission turn of the
scanning response in a transmission order of a plurality of scanning
responses responding to the scanning request.

[0009] According to yet another aspect of the present invention, there is
provided a computer program product embodied on a distribution medium
readable by a computer and comprising program instructions which, when
loaded into the computer, execute a computer process comprising:
acquiring, in an access node of a wireless network, neighbour access node
information comprising at least one of identification, geographical
location, and characteristics of at least one neighbouring access node;
acquiring a scanning request message originated from a requesting device;
determining, at least partly on the basis of the neighbour access node
information, a transmission order of a plurality of scanning responses
that respond to the scanning request; and causing the access node to
transmit a scanning response during a transmission turn of the access
node determined from the transmission order.

[0010] According to yet another aspect of the present invention, there is
provided a computer program product embodied on a distribution medium
readable by a computer and comprising program instructions which, when
loaded into the computer, execute a computer process comprising: causing
a scanning device to transmit a scanning request comprising context
information to a plurality of access nodes; acquiring in the scanning
device a scanning response from an access node, wherein the scanning
response comprises an information element indicating a transmission turn
of the scanning response in a transmission order of a plurality of
scanning responses responding to the scanning request.

[0011] Embodiments of the invention are defined in the dependent claims.

LIST OF DRAWINGS

[0012] Embodiments of the present invention are described below, by way of
example only, with reference to the accompanying drawings, in which

[0013] FIG. 1 illustrates a communication scenario to which embodiments of
the invention may be applied;

[0014] FIG. 2 illustrates a signalling diagram of an embodiment for
determining a transmission order for a plurality of scanning response
messages according to an embodiment of the invention;

[0015] FIG. 3 is a flow diagram related to an embodiment where identifiers
of access nodes are used when determining the transmission order
according to an embodiment of the invention;

[0016] FIG. 4 is a flow diagram related to an embodiment where locations
of the access nodes are used when determining the transmission order
according to an embodiment of the invention;

[0017] FIG. 5 illustrates an embodiment where the number of responding
access nodes is limited by using a geographical limitation according to
an embodiment of the invention;

[0018] FIG. 6 is a flow diagram related to an embodiment where service
characteristics of the access nodes are used when determining the
transmission order according to an embodiment of the invention;

[0019]FIG. 7 is a flow diagram related to an embodiment where multiple
criteria are used when determining the transmission order according to an
embodiment of the invention;

[0020] FIG. 8 is a flow diagram related to an embodiment where the
transmission order is updated according to an embodiment of the
invention;

[0021] FIG. 9 is a flow diagram of a process carried out in a scanning
device for detecting a number of missed scanning responses according to
an embodiment of the invention; and

[0022] FIGS. 10 and 11 illustrate block diagrams of apparatuses according
to some embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

[0023] The following embodiments are exemplary. Although the specification
may refer to "an", "one", or "some" embodiment(s) in several locations,
this does not necessarily mean that each such reference is to the same
embodiment(s), or that the feature only applies to a single embodiment.
Single features of different embodiments may also be combined to provide
other embodiments. Furthermore, words "comprising" and "including" should
be understood as not limiting the described embodiments to consist of
only those features that have been mentioned and such embodiments may
contain also features/structures that have not been specifically
mentioned.

[0024] A general architecture of a wireless communication system to which
embodiments of the invention may be applied is illustrated in FIG. 1.
FIG. 1 illustrates wireless communication devices forming wireless
networks that may be referred to as service sets. A basic service set
(BSS) may be defined by a group of wireless communication devices
comprising an access point (AP) 102, 104, 106 and one or more terminal
stations (STA) 110 communicating with one of the access points 102, 104,
106 depending on with which BSS the STA associates to for frame
transmission. The BSS is a basic building block of an IEEE 802.11
wireless local area network (WLAN), and it may have a determined coverage
area defined by the coverage area of the AP 102, 104, 106, for example.
The most common BSS type is an infrastructure BSS that includes a single
AP together with all associated, non-access-point STAs. The AP may be a
fixed AP as APs 102, 104, 106, but it should be appreciated that in some
embodiments at least one of the APs 102 to 106 may be a mobile AP. The
APs 102, 104, 106 may also provide access to other networks, e.g. the
Internet. In another embodiment, at least one of the BSSs is an
independent BSS (IBSS) or a mesh BSS (MBSS) without a dedicated AP, e.g.
the communication device 106 may in such an embodiment be a
non-access-point terminal station. Yet another embodiment of the service
set is an extended service set (ESS) which may be defined as a set of one
or more interconnected BSSs that appear as a single BSS to the STAs. In
the scenario illustrated in FIG. 1, the AP 106 serves as a single access
point of a BSS, while APs 102, 104 form an ESS comprising a plurality of
APs. The coverage areas of the respective service sets are shown by the
dotted line in FIG. 1.

[0025] While embodiments of the invention are described below in the
context of the above-described topologies of IEEE 802.11, it should be
appreciated that other embodiments of the invention are applicable to
networks based on other specifications, e.g. WiMAX (Worldwide
Interoperability for Microwave Access), UMTS LTE (Long-term Evolution for
Universal Mobile Telecommunication System), and other networks having
cognitive radio features, e.g. transmission medium sensing features and
capability to adopt operational parameters to enable coexistence with
radio access networks based on different specifications and/or standards.

[0026] The service sets are represented by the APs and/or STAs connected
to each other, thereby establishing a service set which may be a BSS,
IBSS, MBSS, or ESS. The STA 110 may establish a connection to any one of
the APs 102, 104, 106. The connection establishment may include
authentication in which an identity of a STA is established in the AP.
The authentication may comprise exchanging an encryption key used in the
BSS. After the authentication, the AP and the STA may carry out
association in which the STA is fully registered in the BSS, e.g. by
providing the STA with an association identifier (AID) for frame
transmissions.

[0027] The APs 102 to 106 may establish a signalling interface for
exchanging any information relevant for the coexistence of the APs 102 to
106. This signalling interface is represented in FIG. 1 by a distribution
system (DS) 120. The DS may be a wired backbone providing wired
connections between the APs 102 to 106, and/or at least some of the links
of the DS 120 may be wireless, e.g. in a case of mobile APs. An AP may
provide the other APs with information on its communication parameters,
information on other BSSs that the AP has discovered and their respective
communication parameters, etc. In an embodiment, the DS 120 is provided
only amongst the APs of the same ESS, while in other embodiments the DS
120 is provided also between the different service sets. In the former
embodiment, at least some of the information exchanged over the DS 120
may be exchanged over the radio interface between the different service
sets. In this context, the information may be included in channel access
coordination information element to be transmitted as part of the
management frames such as beacon frames, measurement pilot frames, and
other scanning messages.

[0028] In some embodiments, at least some of the APs 102 to 106 are
connected to a server controlling at least some of the operations of the
APs. The server may provide centralized control of at least some of the
communication parameters of the APs. The connections between the APs and
the server may be realized through the DS 120. The server may be an ESS
server controlling the operation of APs within the same ESS, for example.
In another embodiment, the server controls the operation of APs belonging
to different service sets or different wireless networks.

[0029] An 802.11n specification specifies a data transmission mode in
which a STA can have only one secondary channel which results in a
maximum bandwidth of 40 MHz. The primary channel is used in all
transmissions, and with associated devices supporting only the 20 MHz
mode. The secondary channel may be used with clients supporting wider
transmission bandwidths, wherein the primary channel communication is
extended by using the secondary channel as additional bandwidth. A
further definition in the 802.11n is that the primary and secondary
channels are adjacent. The IEEE 802.11ac task group is developing an
extension with a data transmission model to provide for wider bandwidths
by increasing the number of secondary channels from 1 up to 7, thus
resulting in bandwidths of 20 MHz, 40 MHz, 80 MHz, and 160 MHz.

[0030] The primary channel may be used for connection establishment
leading to association between two wireless apparatuses between which the
connection is to be established. A wireless apparatus preparing for the
association may scan for channels in order to detect a signal indicating
presence of another wireless apparatus for association. The wireless
apparatus may be in a completely unassociated state or it may have at
least one existing association while seeking for a reassociation. IEEE
802.11 network discovery mechanisms define two modes: passive and active
scanning. In the passive scanning, the wireless apparatus scans a channel
for up to a maximum period of time. If a wireless network is discovered
by detecting a scanning message transmitted by the wireless network, the
wireless apparatus may proceed to connection establishment or, otherwise,
it may tune to another channel. The scanning messages the wireless
apparatus may scan for comprise beacon frames, measurement pilot frames,
or any other frames. The measurement pilot frame may be defined as a
short action frame comprising a subset of information contained in the
beacon frame, but the measurement pilot frame may be transmitted more
frequently than the beacon frames. The frames may be originated from any
AP or destined to any AP or, alternatively, the wireless apparatus scans
for frames that meet the given criteria e.g. a determined identifier,
such that the wireless apparatus is able to detect any wireless network,
including IBSSs and mesh BSSs. When the wireless apparatus uses the
active scanning, it generates a probe request frame and transmits the
probe request frame in order to request APs or, in general, other
wireless apparatuses to reply with probe response frames. The probe
response frames may thus also be considered to be scanning messages the
wireless apparatus is attempting to detect. The rules applied to the
requesting device (e.g. a STA) and the responding device (e.g. an AP)
during the active scanning may be defined as follows. Upon tuning to a
new channel, e.g. a new frequency channel, the requesting device may
first scan the channel for a determined period of time, e.g. a probe
delay, or until it detects a frame header, e.g. a physical layer
convergence protocol (PLCP) header, on the channel. Thereafter, the
requesting device may initiate a channel contention so as to gain a
transmission opportunity for transmission of a probe request frame. The
requesting device may transmit one or more probe request frames
comprising information (for example, a service set identifier (SSID)
field and/or a BSS identifier field) specifying which wireless apparatus
may respond to the probe request. The requesting device may also reset a
probe timer to zero and start it upon transmitting the probe request. If
the requesting device detects no WLAN signal with sufficiently high
energy on the channel on which the probe request was transmitted before
the probe timer reaches a minimum probe response time, it tunes to a next
channel. Otherwise, the requesting device may wait on the channel until
the probe timer reaches a maximum probe response time and, thereafter,
the requesting device processes all received probe responses. Optionally,
the requesting device may then tune to scan the next channel. The probing
procedure provides the requesting device with information on the wireless
networks present in the area and, as a consequence, enables the
requesting device to select a wireless network with which to establish a
connection. The responding device receiving the probe request may respond
with a probe response if an address field in the probe request frame is a
broadcast address, an individual medium access control (MAC) address of
the responding device, or a multicast address of the responding device.
Another condition for causing the responding device to transmit the probe
response is that the SSID in the probe request is a so-called wildcard
SSID, the specific SSID of the responding device, or the specific SSID of
the responding device is included in an SSID list element of the probe
request. Yet another condition may be that the specific Mesh ID in the
probe request is the specific Mesh ID of the responding device, or an
address 3 field in the probe request is a wildcard BSSID, the BSSID of
the responding device, or the MAC address of the peer device in a mesh
BSS. Further conditions for responding to the probe request may also be
set. In general, the probe request specifies the conditions defining the
devices that should respond with the probe response. All devices that
fulfil the conditions may attempt to transmit the probe response frame.

[0031] In general, the APs may transmit the scanning responses as
responses to scanning requests received from scanning devices, e.g.
scanning STAs. When the number of APs in the coverage area of the
scanning device is high, the number of scanning responses may increase to
such dimensions that the signalling overhead caused by the high number of
scanning responses increases as does the channel contention the APs carry
out in order to gain channel access to transmit their respective scanning
responses. This increases the probability of collisions and increases
scanning response total delays. Let us now consider an embodiment of the
invention with reference to a signalling diagram of FIG. 2. The
signalling diagram illustrates a process for reducing the signalling
overhead caused by the probe responses by determining the transmission
order of the scanning responses and reducing channel contention time upon
determining the transmission order. The signalling diagram comprises
steps carried out in an access node, e.g. any one of the APs 102 to 106,
and steps carried out in a scanning device, e.g. the STA 110. Referring
to FIG. 2 neighbour access node information comprising at least one of
identification, geographical location, and characteristics of at least
one neighbouring access node is acquired in the access node in block 200.

[0032] In block 202, the scanning device carries out an active scanning
procedure and causes transmission of a scanning request message. In an
embodiment, the scanning request message comprises context information,
e.g. a location of the scanning device and/or service requirements of the
scanning device. In other embodiments, the scanning request message of
block 202 is a conventional scanning request message. In block 204, the
scanning request message originated from the scanning device is acquired
in the access node. Let us assume that the scanning request message
specifies such conditions that obligate the access node to respond to the
scanning request message with a scanning response message. Therefore, in
block 206, a transmission order of a plurality of scanning responses that
respond to the scanning request is determined at least partly on the
basis of the neighbour access node information acquired in block 200. In
some embodiments, block 206 comprises determining the transmission order
also on the basis of the context information acquired from the scanning
request message in block 202. On the basis of the transmission order, the
access node is able to determine its transmission turn and, as a
consequence, the access node is configured in block 208 to transmit a
scanning response message during a transmission turn of the access node
determined from the transmission order in block 206. The scanning
response message of block 208 is the response to the scanning request of
blocks 202 and 204. In block 210, the scanning device acquires the
scanning response message.

[0033] In an embodiment, the scanning response message comprises an
information element indicating the transmission turn of the scanning
response message, and the scanning device may process the information
element in block 210. The scanning device may use the information element
to determine if one or more scanning responses have not been received, as
will be described in greater detail below.

[0034] In an embodiment, the access nodes exchange their transmission
turns over the DS 120 in order to ensure that the same transmission turn
is not allocated to two access nodes. In another embodiment, a central
server may carry out the procedure of FIG. 2 and distribute the
transmission turns to the access nodes over the DS 120.

[0035] When the access node and other access nodes determine the
transmission order of the scanning responses, the channel contention
according to carrier sensing multiple access with collision avoidance
(CSMA/CA), distributed coordination function (DCF), or enhanced
distributed channel access (EDCA) may be avoided or at least reduced. For
example, the duration of which an access node needs to sense the channel
to be free before transmitting the scanning response message may be
shorter than a sensing duration of another message for which no
transmission order has been determined. In an example related to IEEE
802.11 networks, if no transmission order has been determined, the access
node may need to sense the channel to be free for a duration of a DCF
inter-frame space (DIFS) plus an additional random backoff time, and this
duration may be reduced to a shorter duration such as point coordination
function inter-frame space (PIFS) or short inter-frame space (SIFS) in
the embodiment of FIG. 2. In some embodiments, the backoff time may even
be omitted to reduce the channel contention. In an embodiment, the access
node may determine whether or not its transmission turn is the first
transmission turn in the transmission order determined in block 206. If
the access node has the first transmission turn, it may apply a longer
guard time and/or the backoff time before carrying out the transmission
of the scanning response message than in a case where the transmission
turn of the access node is not the first transmission turn. As a
consequence, normal channel contention may be applied to the first
transmission turn, but any subsequent transmission turn may be carried
out without or at least with the reduced channel contention, e.g. with
the reduced guard time and/or without the backoff time.

[0036] With respect to determining the actual transmission timing of its
transmission turn, the access node may monitor the scanning response
messages transmitted by the neighbouring access node as a response to the
scanning request message. Assuming that the transmission turn of the
access node is X, upon detecting a scanning response message comprising
the transmission turn indicator indicating a transmission turn X-1, the
access node may proceed to transmit its scanning response in the next
transmission opportunity. If the access node does not detect the
preceding scanning response message for some reason, it may carry out a
normal channel contention in order to transmit the scanning response
message, e.g. through the EDCA procedure. The channel contention may be
triggered upon detecting no scanning response of the transmission turn
X-1 within a determined time interval after the previous scanning
response of the transmission turn X-2, for example. The determined time
interval may be selected sufficiently short such that the access node may
still transmit the scanning response during its transmission turn. For
example, the determined time interval may be higher than the guard
interval between consecutive scanning response messages, e.g. a PIFS or
SIFS, but shorter than the guard interval plus the duration of the
scanning response message. This ensures that the missed detection of a
previous scanning response message is not propagated to the access nodes
having a later transmission turn.

[0037] In another embodiment where a plurality of responding access nodes
waiting for their transmission turn and monitoring for the scanning
response messages detect no scanning response message in an arbitrary
transmission preceding their transmission turns, the channel contention
may be triggered in all the responding access nodes. From the point of
view of a single access node, the access node may monitor for the
scanning response messages of all transmission turns preceding its own
transmission turn and, upon detecting no scanning response message in one
these preceding transmission turns, the access node may trigger the
channel contention in order to transmit the scanning response message
even before its actual transmission turn. The channel contention may
follow the EDCA procedures, and the access node may determine its backoff
time from its transmission turn, for example. In an embodiment, the
higher is the transmission turn value of the access node, the longer is
the backoff time the access node has to wait for the channel to be free
before gaining the transmission opportunity for the scanning response
message. In another embodiment, the EDCA parameters of the group of
contending responding access nodes are selected according to the number
of contending responding access nodes, e.g. how much randomness is needed
to randomly select non-colliding transmission times. The computation of
the backoff time may be started upon making a decision that a scanning
response message of a previous transmission turn has been missed or,
alternatively, the computation of the backoff time may be started even
when the access node is still scanning for the previous scanning response
message, e.g. before the decision about missing the previous scanning
response message has been missed. The latter option speeds up the channel
contention by "emulating" the channel contention even before the channel
contention is actually triggered. The access node may, however, prevent
transmission of its own scanning response message before making the
decision. Such embodiments where missed detection of a previous scanning
response message triggers the channel contention in the responding access
node also ensures that the missed detection of the previous scanning
response message does not propagate to the access nodes having a later
transmission turn.

[0038] In another embodiment, the access node may derive its transmission
timing by monitoring for scanning response messages of other access nodes
having a prior transmission turn. Upon detecting a scanning response
message from a specific MAC address associated with the preceding
transmission turn, the access node may determine that it has the next
transmission turn and it may trigger the transmission of the scanning
response message. In this embodiment, the access node associates the
transmission turns with the MAC addresses of the neighbouring access
nodes and monitors for the MAC addresses of the detected scanning
response messages in order to determine its transmission turn.

[0039] In another embodiment, the access node may derive its transmission
timing directly from the transmission turn when it has the knowledge of
the lengths of all the preceding scanning responses. For example, the
scanning response message may have a constant length, or the length
information may be exchanged over the DS 120. The computation of the
transmission timing may take into account the lengths of the previous
scanning response messages and any possible guard intervals between them.
For example, when the transmission turn is 3, the transmission timing may
be computed as: DIFS+Average Backoff Time+Length of the 1st Response
including an acknowledgment to the 1st Response+(P/S)IFS+Length of
the 2nd Response including an acknowledgment to the 2nd
Response+(P/S)IFS, assuming that all responses have been detected
successfully. After the expiry of this time interval, the access node may
determine that it is its transmission turn. However, if the exact
transmission timing cannot be computed because of insufficient knowledge
about the length or transmission status of the previous scanning
responses, for example, the access node may carry out the procedure
described above in the previous paragraph. This embodiment may be used
within access nodes of the same ESS, e.g. an access node of an ESS may
determine its transmission timing within the ESS in the above-described
manner. A normal channel contention based on EDCA principles, for
example, may be carried out between ESSs to gain the transmission
opportunity for the scanning response messages within the ESS. In other
words, the ESS winning the contention may continue to transmit all of its
scanning response messages before the other ESS(s). In another
embodiment, the ESS with the largest number of responding access nodes,
which is available from the channel access coordination information
element in Table 5 below, may transmit first without channel contention.
Thereafter, the access nodes having subsequent transmission turns within
the ESS may compute their actual transmission timings in the
above-described manner. In a further embodiment, the first response
message of the transmission order within the ESS or between service sets
may be a long response message comprising parameters of at least some or
even all of the access nodes having the following transmission turns,
while the following scanning response messages comprise less information,
e.g. a minimum set of information required for the scanning response
message.

[0040] In any one of the above-described embodiments where the access
node(s) is/are configured to detect the missed transmission of a scanning
response message and to start the channel contention, the channel
contention may first be carried out on a service set level. For example,
a subset of access nodes of an ESS may start the channel contention upon
detecting a missed scanning response message. Let us assume that one of
the access nodes wins the channel contention and gains a transmission
opportunity to transmit a scanning response message. Upon detecting that
their ESS won the contention, the other access nodes of the ESS may be
configured to carry out subsequent channel contentions with such EDCA
parameters that provide the fastest channel access, e.g. the shortest
backoff time. The use of the optimal EDCA parameters may be stopped upon
detecting an intervening transmission by another device that is not party
of the ESS. The intervening transmission may be detected after the ESS
has won the contention but before all the access nodes of the ESS have
had the chance to transmit the scanning response message. Let us assume
that another ESS wins a contention between the scanning response
transmissions of the ESS in question. Then, the option to use the optimal
EDCA parameters may be passed to the other ESS, and upon detecting the
won channel contention in an access node of the other ESS, the access
node of the other ESS may implement the optimal EDCA parameters in a
subsequent scanning response transmission. In summary, the missed
detection of the previous scanning response in the transmission order may
trigger the channel contention on the service set level, and winning the
channel contention in a service set may trigger utilization of high
priority or optimal EDCA parameters that provide fast channel access,
thereby reducing the contention overhead.

[0041] In an embodiment where the access nodes utilize a retry limit to
retransmit the scanning response messages in case the access node does
not receive an ACK frame. The retry limit may be set to 0 to disable the
retransmissions in order to avoid collisions. The retransmissions may be
disabled for broadcast-addressed frames but also for frames addressed to
another address than the broadcast address. Instead, the transmission of
a new scanning request may be initiated by the scanning device upon
determining from the transmission turn indicator, for example, that it
has missed at least one scanning response message (see embodiment of FIG.
9 below), thus enabling the retransmission functionality. In another
embodiment where the retransmissions are not disabled, an access node
waiting for its transmission turn may be configured to acquire the
preceding probe response and associated acknowledgment or at least the
acknowledgment of the preceding probe response before initiating its
transmission turn.

[0042] In an embodiment, block 206 comprises a sub-routine where the
access node is configured to filter the neighbouring nodes included in
the determination of the transmission order on the basis of the
conditions defining the responding devices included in the scanning
request message. The access node may be configured to compare the
parameters of the neighbouring access nodes with the conditions defined
in the scanning request message and determine the neighbouring access
nodes that are obliged to respond to the scanning request. Then, only
those access nodes that are obliged to transmit the scanning response
message may be taken into account when determining the transmission order
in block 206.

[0043] In an embodiment, the scanning device includes in the scanning
request a number of scanning responses it chooses to receive.
Accordingly, the access node may include/remove itself to/from the
transmission order based on the number of scanning responses indicated in
the scanning request message. The access node may determine whether or
not its own transmission turn value is higher than the number of scanning
responses indicated in the scanning request message. If the transmission
turn value of the access node is higher than the number of scanning
responses indicated in the scanning request message, the access node may
prevent the transmission of the scanning response message. Otherwise, it
may carry out the transmission of the scanning response message in block
208, as described above.

[0044] In an embodiment, the scanning request message is the probe request
message of an IEEE 802.11 network, and the scanning response message is a
probe response message of the IEEE 802.11 network.

[0045] Let us now consider some embodiments for determining the
transmission order in the access node with reference to FIG. 3 to 8. In
some embodiments, the transmission order is determined by using a static
parameter as a criterion, and such an embodiment may be called a
policy-based approach. In other embodiments, the transmission order is
determined by using semi-static or dynamic parameters as a criterion or
criteria, and such an embodiment may be called a parameter-based or
context-sensitive approach.

[0046] FIG. 3 illustrates an embodiment of a policy-based approach where
identifiers of the access nodes are used to determine the transmission
order. As mentioned above, the access nodes (e.g. APs 102 to 106) may be
aware of any neighbouring access node through signalling over the DS 120
and/or over a radio interface. The access nodes may constantly transmit
beacon frames, measurement pilot frames, and/or other management frames
that comprise their identifiers and any relevant information on them. As
a consequence, the access nodes gain information on the identifiers,
capability information, and operational parameters of neighbouring access
nodes. Such information may be exchanged a priori in block 200 through
the DS 120 via inter-AP protocol (IAPP) in the background, or it may be
stored in a network management database which is updated periodically and
subsequently shared to all the APs having access to the database. Hence,
an AP may gain knowledge of the all other APs in the same ESS through
information exchange via the DS and of any other neighbouring AP through
information exchange via the DS and/or the radio interface. Referring to
FIG. 3, the access node acquires identifiers of the neighbouring access
nodes as the neighbour access node information in block 300. In an
embodiment, the identifier is a medium access control (MAC) address. Upon
receiving the scanning request in block 204, the access node determines
the transmission order from the identifiers in block 302. In an
embodiment, the transmission order is determined from the identifiers by
processing the identifier values of the access node and the neighbouring
access nodes as such, e.g. by sorting the identifier values into an
ascending or descending order, or by sorting them according to another
predefined rule. When the neighbouring access nodes also carry out block
302, the access node may apply the same predefined rule as the
neighbouring access nodes. Upon sorting the identifier values and
acquiring a sorted list of identifiers, the access node may count its
transmission turn from the location of its own identifier in the sorted
list of identifiers. Upon determining its transmission turn, the access
node may carry out the transmission of the scanning response during its
transmission turn in block 208.

[0047] FIG. 4 illustrates a flow diagram of an embodiment using the
context-sensitive approach by using positioning as a tool for determining
the transmission order. Referring to FIG. 4, the access node may acquire
the locations of the neighbouring access nodes in block 400. The format
in which the location is described may be arbitrary, e.g. satellite
system (GPS; GLONASS, Galileo) coordinates, any other geolocation
coordinates, or any other positioning coordinates. In block 202 (FIG. 2),
the scanning device transmits the scanning request. In this embodiment,
the scanning request may comprise an information element indicating the
location of the scanning device. The location information contained in
the scanning response may be in the same format as the format of the
location information in block 400. In block 204, the access node acquires
the scanning request message and extracts the location of the scanning
device from the scanning request message.

[0048] In block 402, the access node may compute the relative positions of
the access node itself and the neighbouring access nodes to the scanning
device and determine the transmission order by sorting the relative
positions into an ordered list according to a predefined rule, e.g. in an
ascending or descending order. In an embodiment using the ascending
order, the access node having the shortest relative position to the
scanning device gets the first transmission turn, the access node having
the second shortest relative position to the scanning device gets the
second transmission turn, and so on. The embodiment using the ascending
order has the advantage that the scanning device acquires the scanning
responses first from the access nodes that probably can provide the best
radio link with the scanning device. The relative position may be
computed according to state of the art techniques, e.g. according to
Equation (1):

Depending on whether the format of the location information utilizes
two-dimensional (2-D) or three-dimensional (3-D) coordinates, one of the
options for computing the relative position Δi of Equation (1)
may be selected. Instead of using the Cartesian coordinates of the two
locations, e.g. the location of the scanning device defined by
coordinates [x1, y1, z1] and the location of the i-th
access node defined by coordinates [x2,i, y2,i, z2,i], as
in Equation (1), the computation may be carried out by using any other
coordinates, e.g. sphere coordinates or Geodetic coordinates according to
World Geodetic System-84 (WGS-84). Note that instead of the relative
position, Equation (1) may be understood as a computation of relative
distances between the scanning device and the access nodes, and the
relative distance may be used in determining the transmission order.

[0049] In an embodiment where the scanning device limits the number of
scanning responses, the limitation may be based on the actual number
value defining the number of scanning responses or the limitation may be
based on the geolocation, as described now with reference to FIG. 5. The
scanning device may include in block 202 in the scanning request message
an information element that specifies a discovery range. The discovery
range may define a perimeter around the scanning device, and only the
access nodes that are located within the perimeter are obliged to
respond, provided that those access nodes also comply with any other
conditions set out in the scanning request message. FIG. 5 illustrates an
embodiment where the access nodes 102 and 104 are located within the
discovery range, while the access node 106 is outside the discovery
range. Therefore, even though the access node 106 is able to detect the
scanning request and meets the other conditions set out in the scanning
request, it will not respond to the scanning request message, and it will
be excluded when determining the transmission order for the scanning
response messages in block 402, for example.

[0050] In an embodiment, the discovery range is smaller than the
communication range of the scanning device, as shown in FIG. 5. In an
embodiment, the scanning device is configured to compute a discovery zone
defined by the discovery range is defined as:

r discovery = R tx 2 r * ( 2 ) ##EQU00002##

where rdiscovery is the discovery range in the form of a radius, for
example, Rtx is the transmission range of the scanning device which
may be preset and stored beforehand in the scanning device, and r* is a
scaling factor having a value between 0 and 1, for example. In this
embodiment, the discovery range is at most half of the communication
range of the scanning device. Reducing the discovery range provides the
advantage that it improves the probability that all access points within
the discovery range are able to detect each other and, thus, effects of a
hidden access node problem are eliminated or at least reduced.

[0051] Another embodiment utilizes characteristics of the access nodes to
determine the transmission order for the scanning response messages. The
characteristics may comprise operational parameters or service parameters
of the access nodes. Referring to a flow diagram of FIG. 6, such service
parameters of the access node and the neighbour access nodes are acquired
in block 600. Such parameters may comprise any metric related to a
current load or capacity of the access nodes, e.g. data rate, throughput,
buffer occupancy, packet delay, and packet loss. In an embodiment, a
plurality of characteristics may be combined to provide a service quality
metric as the service parameter. Then, the scanning device transmits in
block 202 (FIG. 2) the scanning request message, and it may include in
the scanning request message in information element specifying service
requirements of the scanning device. The service requirements may be
provided in the form of an access class or quality-of-service (QoS)
class, but other service requirements are naturally possible. The service
requirements specified by the scanning device may be compatible with the
service parameters defined in block 600, or there may be a correspondence
between them such that the access node is able to map the service
requirements to the service parameters. In block 204, the scanning
request message is acquired in the access node, and the service
requirements are extracted from the scanning request message. In block
602, the service parameters acquired in block 600 are sorted, and the
transmission order is determined from the sorted list. The sorting may
comprise a first step where those access nodes that are not able to meet
the service requirements are excluded, and a second step where the
remaining access nodes that are able to meet the service requirements are
ordered, for example, on the basis of how well they meet the service
requirements. In an embodiment, an access node capable of providing the
scanning device with the highest service quality gets the first
transmission turn and so on. The highest service quality may be defined
as the highest available capacity which may be inferred from the lowest
buffer occupancy, the highest throughput or data rate, or the lowest
packet loss or packet delay. As a consequence, the access node acquires
its transmission turn and may carry out the transmission of the scanning
response during its transmission turn in block 208.

[0052] In the embodiments described above in connection with FIGS. 4 to 6
where the access node closest to the scanning device or having the
capability that best meet with the service requirements gets the first
transmission turn, the transmission order itself indicates to the
scanning device those access nodes that are the most promising candidates
for the association. Accordingly, the scanning device may prefer the
access nodes from which it receives the scanning response first. In an
embodiment, the scanning device may even be configured to cancel the
scanning process upon selecting an access node with which to associate.
To this end, the scanning device may be configured to transmit a scanning
termination message, e.g. a Probe End frame instead of an ACK frame,
thereby cancelling any subsequent scanning response transmission or
transmissions of the transmission order. An access node that has not yet
had its transmission turn and detecting the scanning termination message
may cancel its transmission turn and, as a consequence, prevent the
transmission of the scanning response message.

[0053] In an embodiment, the transmission order is determined from a
plurality of input parameters that are combined in a determined manner.
FIG. 7 illustrates a flow diagram of an embodiment where the relative
positions between the access nodes and the scanning device are the first
input parameter, and this first input parameter is then weighted with a
second input parameter which may comprise, for example, the
above-described service parameter(s) and/or any other conditions set out
in the scanning request message. Referring to FIG. 7, the access node
acquires the locations of the neighbour access nodes in block 400 and the
scanning request message in block 204. Depending on the embodiment, the
scanning request may comprise the location of the scanning device and,
optionally, the service requirements. In block 702, the access node may
determine the relative positions Δ between each access node and the
scanning device in the above-described manner. As a result, the access
node acquires a set of distance values {Δ1, Δ2, . .
. , Δk}. The distance values may then be used as such in the
sorting, or the access point may normalize the relative position values
according to Equation (3):

Δ i * = UB - Δ i UB - LB ( 3 )
##EQU00003##

where UB is a maximum value in the set of relative position values
{Δ1, Δ2, . . . , Δk}, and LB is a
minimum value in the set of relative position values {Δ1,
Δ2, . . . , ΔK}. As a result of computing Equation
(3), an access node closest to the scanning device gets a value 1, while
an access node having the greatest distance to the scanning device gets a
value 0.

[0054] In block 704, the access node then weighs the acquired normalized
relative position values according to another criterion or criteria, thus
acquiring decision metrics for the sorting operation. The access node may
multiply each normalized relative position value with a priority factor
which may be derived according to the matching between the service
requirements set out in the scanning request message and the
characteristics of the access nodes. Alternatively, or additionally, the
priority factor may be derived according to matching between the
conditions for the obligation to respond set out in the scanning request
and the characteristics of the access nodes. The priority factor may be
proportional to a percentage how well each access node is able to match
with the service requirements and/or the conditions. In an embodiment,
the value of the priority factor may be between 0 and 1. Then, the
transmission order may be determined from these weighted decision metrics
by sorting them according to a determined criterion. The sorting may
again be arranged such that the access nodes being closest to the
scanning device and being able to best meet the service requirements
and/or conditions gain the first transmission turn(s), while the access
nodes far away from the scanning device and not being able to well meet
the service requirements and/or conditions gain the last transmission
turns or even no transmission turn at all. For example, if the closest
access node gains the lowest normalized relative position according to
Equation (3), the weighing may assign a lower priority factor to those
access nodes that best meet the service requirements and/or conditions,
and the decision metrics may be sorted into an ascending order such that
an access node with the lowest decision metric value gains the first
transmission turn.

[0055] The embodiments described above in connection with FIG. 7 have an
advantage in that improve the probability that the access nodes having
the best capability of serving the scanning device gain the opportunity
to transmit the scanning response message before the access nodes not
capable of well serving the scanning device.

[0056] During operation of the wireless network and the access nodes,
there may exist situations where an access node is not able to transmit
the scanning response message for some reason or another. In order to
avoid unused transmission turns, the access node may be configured to
update the transmission order, when necessary. FIG. 8 illustrates a flow
diagram of an embodiment for updating an initial transmission order
determined in block 206, 302, 402, 602, or 706, for example. In the
embodiment of FIG. 8, block 206 is used as an example. In block 802, the
access node detects that at least one of the access nodes having a
transmission turn in the transmission order skips its transmission turn.
The at least one skipping access node may be at least one neighbouring
access node. The reason for skipping the transmission of the scanning
response message may be that the access node determines that its traffic
load is so high that it does not want to serve further terminal devices,
or it may detect that the matching between the service requirements and
its service characteristics is not sufficient. Upon determining to skip
the transmission turn, the skipping access node may be configured to
transmit an appropriate signal through the DS 120 and, as a consequence,
the detection in block 802 may be based on reception of such a signal
through the DS 120. In an embodiment, the signal comprises an information
element that indicates that the transmission turn of the skipping access
node is zero (0). Upon receiving the signal indicating that the
transmission turn of a neighbouring access node is 0, the access node
knows that the access node with response order 0 will be skipped in the
transmission order, and it may update the transmission order in block 804
by removing the skipping access node's transmission turn and decrementing
the transmission turn of all access nodes having a transmission turn
after the transmission turn of the skipping access node. Thus, the
transmission order remains contiguous and without unused transmission
turns. Then, the access node may transmit its scanning response during
its transmission turn determined from the updated transmission order.

[0057] As mentioned above, the scanning response messages transmitted by
the responding access nodes may comprise the information element
indicating the transmission turn of each scanning response message. This
enables the scanning device to monitor the scanning response messages and
to determine whether or not it has received all the scanning responses.
Upon detecting that consecutively detected scanning response messages do
not have consecutive transmission turn indicators, the scanning device
may determine that at least one scanning response has been missed. FIG. 9
illustrates an embodiment of such a procedure for detecting missed
scanning response messages in the scanning device. Referring to FIG. 9,
the scanning device transmits the scanning request message in block 202.
The scanning request message may be any one of the above-mentioned
scanning requests, e.g. it may or may not comprise the context
information, e.g. the location of the scanning device and/or the service
requirements. In block 900, the scanning device initializes a
transmission turn counter. Block 900 may also comprise initialization of
a missed scanning response counter. In block 210, the scanning device
acquires the first scanning response message that responds to the
scanning request message of block 202. In block 902, the scanning device
extracts from the acquired scanning response message the transmission
turn indicator. In block 904, the scanning device compares the
transmission turn indicator value with the transmission turn counter. If
the values match, it is determined that no scanning response messages
have been missed, and the process proceeds to block 908 in which the
transmission turn counter is incremented by one and the scanning device
returns to monitor for a next scanning response message. Upon detecting
the next scanning response message, the process proceeds in block 210.

[0058] However, if the transmission turn indicator value and the
transmission turn counter in block 904 are different, this means that
there has been at least one scanning response message preceding the
currently processed scanning response message that has not been detected
by the scanning device. As a consequence, the process proceeds from block
904 to block 906 in which the missed scanning response counter is
incremented. The increment is determined on the basis of the difference
between the transmission turn indicator value and the transmission turn
counter. For example, if the transmission turn indicator value minus the
transmission turn counter equals to two, two scanning responses have been
missed, and the missed scanning response counter is incremented by two.
Then, the process proceeds to block 908 in which the transmission turn
counter is incremented by the same amount as the value of the number of
missed scanning responses in block 906. In this manner, the transmission
turn counter is updated to an appropriate value by taking into account
the number of missed scanning responses.

[0059] Upon detecting that the scanning device has missed a determined
number of scanning response messages, it may transmit a new scanning
request message in order to receive the scanning responses from those
access nodes that were not detected during the first active scanning. The
scanning device may also include a filtering list in the new scanning
request so that scanning responses from known wireless networks (as a
result from the first scanning request message) need not be
retransmitted.

[0060] Let us now consider some embodiments of information elements
contained in the above-described scanning request message and scanning
response messages. The access nodes may employ the ordered transmission
of the scanning responses by default, or the scanning request message may
comprise an information element that triggers the ordered transmission of
the scanning responses. In the IEEE 802.11 networks, such an information
element may be dot11_EnhancedProbing, and its value may be set to "true"
to trigger the ordered transmission.

[0061] As mentioned above, the scanning device may add to the scanning
request message an information element comprising the context
information, e.g. the location and/or the service requirements of the
scanning device. With respect to the location, the scanning request
message may comprise an information element of Tables 1 and 2 below. In
this embodiment, the scanning request message is assumed to be a Probe
Request message of IEEE 802.11, and it may be modified to include the
following context information element:

[0063] The number value below each field defines the length of the field
in octets. The ID field identifies the information element. The Length
defines the length of the information element and it may be set to either
to 8 or 29 octets depending on the number of fields included in the
information element. An X-coordinate field contains a 4 octet single
precision floating point value defining the location of the scanning
device in an X domain. A Y-coordinate field contains a 4 octet single
precision floating point value defining the location of the scanning
device in a Y domain. Y and X domains may form the Cartesian coordinates
which is a two-dimensional location value of the scanning device,
Z-coordinate, Radius, Reference Offset, Discovery Zone Radius (DZR),
Other Requirement, and Maximum Responses fields may be optional. Each of
the Z-coordinate field, the Radius field, and the Reference Offset field
may contain a 4 octet single precision floating point value. A
Z-coordinate field may define the location of the scanning device in a Z
domain and it may be used with the Cartesian coordinates to form a
three-dimensional location value of the scanning device. A Radius field
may be used with the Cartesian coordinates to form the circle location
value of the scanning device. Accordingly, the location of the scanning
device may be provided as a point location by using the X, Y and
optionally Z coordinates, or as an area location by providing also the
Radius field. The additional Z-coordinate and Radius fields together may
be used to form the sphere location value of the scanning device. An
additional Reference Offset field may be used to form a relative location
value of the scanning device with respect to the baseline location
defined by the X, Y, (and Z) coordinates. This may be useful in an indoor
environment, wherein a baseline location value includes the X-Coordinate
field and the Y-Coordinate field and may also include the Z-Coordinate
field. The baseline location value may specify a building containing the
relative location of the scanning device, and the Reference Offset could
specify a point within the building, e.g. a centre of the building from
which the offset is measured. A Discovery Zone Radius field may contain a
4 octet single precision floating point value which, together with the X
and Y coordinates defines the above-mentioned discovery range. Note that
a constraint may be imposed to limit the value of the Radius field to be
less than the value of the Discovery Zone Radius field in order to
eliminate or at least reduce the hidden access node problem. In addition,
the knowledge of both the Radius field and the Discovery Zone Radius
field may enable fast determination of transmission order. Let us assume
an example with three access nodes. One access node is located within
both the Radius and Discovery Zone Radius, one access node is located
between the Radius and Discovery Zone Radius, and one access node is
located beyond the Discovery Zone Radius, for example. In this case, the
transmission order may be determined by using both the Radius and
Discovery Zone Radius as ranking thresholds, without computing and
ranking the outcome of Equation (1). An access node computing the
transmission order may assign a prior transmission turn to access node(s)
that is/are located within the area defined by the location of the
scanning device and the Radius zone and a subsequent transmission turn to
access node(s) that is/are located outside the area defined by the
location of the scanning device and the Radius zone and inside the
Discovery Zone Radius. Access node(s) outside the Discovery Zone Radius
may be excluded from the transmission order. The Other Requirement
(Other) field may be used as a 4 octet single precision floating point
value containing the service requirements of the scanning device such as
its required packet delay, packet loss rate, buffer occupancy, or any
statistic that may be mapped to the characteristics of the access nodes,
e.g. the load of the access nodes. The Maximum Responses field may
contain a single octet unsigned integer which provides a criterion to
limit the number of scanning responses.

[0064] In an embodiment where only the service requirements are used as
the context information, the scanning request message may comprise an
information element comprising the Other Requirement field without the
location and discovery range fields of Table 2. The Maximum Responses
field may be included or omitted. In an embodiment using the policy-based
approach, e.g. the identifiers of the access nodes, to determine the
transmission order, even the Other Requirement field may be omitted. The
Maximum Responses field may be included or omitted.

[0065] In another embodiment, the location of the scanning device is
defined as a civic location instead of a geolocation, and the information
element of Tables 1 and 2 may be modified accordingly. For example, Table
2 may be modified into the following form as shown in Table 3.

[0066] Civic Location Type field indicates the format of location
information in the Civic Location field. Optional Subelements field may
comprise zero or more subelements with information that specifies a MAC
address of the scanning device and a target MAC address of the scanning
request message, the format in which the location is provided, e.g. the
shape of the location, and so on as known in connection with IEEE 802.11v
specifications. The civic location field may comprise the actual location
information in the appropriate format.

[0067] In other embodiments, another format of the location is used, and
in each embodiment the format of the information element of Table 1 may
be selected to comply with the location format. The information element
may still comprise any one or more of the fields of Table 2, e.g. the DZR
field and the Maximum Responses field.

[0068] The access node may be configured to insert into the scanning
response message an information element indicating the transmission turn.
The transmission turn information element may carry the transmission turn
of the transmitted scanning response frame so that the scanning device
knows exactly which ordered probe response has not been successfully
received, if any. Additionally, or alternatively, the access node may be
configured to insert into the scanning response message a channel access
coordination information element comprising the neighbour access node
information of block 200. The channel access coordination information
element may contain the geo-location of the responding access node and,
optionally, fields that may be used for coordinating the transmission
order within the discovery zone. Note that the channel access
coordination information element may be included in another scanning
message broadcasted or advertised over the radio interface in order to
advertise the presence of the access node or the ESS. Such a message may
be a beacon frame or a measurement pilot frame, for example. An example
of the information elements added to a conventional scanning response
message, e.g. the Probe Response message of IEEE 802.11, is shown in
Table 4:

[0070] The length field may be set to either 8 or 23 depending on the
fields included in the information elements. The X-coordinate field
contains a 4 octet single precision floating point value defining the
location of the access node in the X domain. The Y-coordinate field
contains a 4 octet single precision floating point value defining the
location of the access node in the Y domain. The Relative Position,
homogeneous ESS ID (HESSID), Number of Responding APs, Response Length,
and Other fields may be optional. The Relative Position field may contain
a 4 octet single precision floating point value which represents the
displacement between the access node and the scanning device along an
imaginary straight line which is the shortest distance between these two
positions. It may be computed according to Equation (1) or (3), for
example, and other access nodes may use the relative position instead of
computing Equation (1) or (3) for each neighboring access node when
determining the transmission order based on the relative position, as
described above. The HESSID field may be a 6 octet MAC address that
identifies a homogeneous ESS, and it may be identical to one of the BSS
IDs in the homogeneous ESS. It may be a globally unique identifier that
may be used in conjunction with the SSID to provide network
identification. The Number of Responding APs field is a single octet
unsigned integer which specifies the number of responding APs of a
specific ESS that are within the discovery zone and that meet the
conditions set out in the scanning request message. The Other field may
be a 4 octet single precision floating point value which may contain
other context information of the access node, e.g. its characteristics
such as the packet delay, packet loss rate, buffer occupancy, or any
statistic that may characterize the load of the access node and that may
be compared with the service requirements of the scanning request
message. With respect to the above-described embodiment where the access
node computes the transmission timing of its transmission turn from the
transmission order beforehand, the channel access coordination
information element may further comprise a Response Length field which
specifies the length of the scanning response messages the access node
uses.

[0071] The Channel Access Coordination information element may be used for
information exchange over the radio interface when an access node does
not have prior location information of neighbouring access nodes that
belong to its own service set or another service set.

[0072] An example of the format of the transmission turn information
element is shown below in Table 6.

TABLE-US-00006
TABLE 6
Element ID Length Transmission Turn
1 1 1

[0073] The length field may be set to 1. The Transmission Turn field may
contain a single octet unsigned integer value comprising the transmission
turn indicator which represents the transmission turn of the scanning
response in the transmission order.

[0074] The Channel Access Coordination and Transmission Turn information
elements may be included in the probe response frame when
dot11_EnhancedProbing is true. Additionally, the Channel Access
Coordination information element may be included in a beacon,
advertisement, or any Action frame.

[0075] FIG. 10 illustrates an embodiment of an apparatus comprising means
for carrying out the above-mentioned functionalities of the access node.
The apparatus may be an apparatus of an IEEE 802.11 network or another
wireless network, e.g. an access point 102, 104, 106 or the central
server controlling the operation of the access points 102, 104, 106. The
apparatus may be a personal computer (PC), a server computer, a laptop, a
tablet computer, a cellular phone, a palm computer, a fixed base station,
or any other device provided with radio communication capability or
controlling the operation of the access points. In another embodiment,
the apparatus is comprised in such a device, e.g. the apparatus may
comprise a physical circuitry, e.g. a chip, a processor, a micro
controller, or a combination of such circuitries.

[0076] The apparatus may comprise a communication controller circuitry 10
configured to control the communications. The communication controller
circuitry 10 may comprise a control part 12 handling control signalling
communication with respect to transmission, reception, and extraction of
control or management messages including the scanning messages. The
control part 12 may handle the reception of the scanning request messages
and transmission of the scanning response messages and other action
frames. The control part 12 may further acquire any knowledge of the
neighbouring access nodes through radio interface and/or through the DS
120. The communication controller circuitry 10 may further comprise a
data part 16 that handles transmission and reception of payload data
during transmission opportunities of the access node (transmission) or
transmission opportunities of other devices (reception). If the apparatus
is the central server, the data part 16 may be omitted unless payload
data is routed through the server, and the control part may handle
exchange of control messages between the server and the access nodes.

[0077] The communication controller circuitry 10 may further comprise a
transmission order controller circuitry 14 configured to determine the
transmission order according to any one of the above-described
embodiments. The transmission order controller circuitry 14 may further
determine the transmission turn of the access node comprising the
apparatus and control the control part 12 to transmit the scanning
responses during the determined transmission turns.

[0078] The communication controller circuitry 10 may further comprise a
timer 18 used to determine the actual transmission timing of the scanning
response messages. The timer 18 may be used to count any guard interval
before the transmission of the scanning response messages and any
interval used to determine that a scanning response message associated
with a preceding transmission turn has not been detected.

[0079] The circuitries 12 to 18 of the communication controller circuitry
10 may be carried out by the one or more physical circuitries or
processors. In practice, the different circuitries may be realized by
different computer program modules. Depending on the specifications and
the design of the apparatus, the apparatus may comprise some of the
circuitries 12 to 18 or all of them.

[0080] The apparatus may further comprise a memory 20 storing computer
programs (software) configuring the apparatus to perform the
above-described functionalities for determining the transmission order
and transmission turn of the scanning response messages. The memory 20
may also store communication parameters and other information needed for
the wireless communications, e.g. the identifiers and any relevant
operational parameters or characteristics of the neighbouring access
point(s) that have been detected. The apparatus may further comprise
input/output (I/O) components 22 providing the apparatus with
communication capabilities. In an embodiment, the I/O components 22
comprise radio interface components 22 providing the apparatus with radio
communication capability with terminal devices, access points, and/or the
server. The radio interface components may comprise standard well-known
components such as amplifier, filter, frequency-converter, (de)modulator,
and encoder/decoder circuitries and one or more antennas. In another
embodiment, the I/O components 22 provide the apparatus with wired
communication capability to communicate with access points and the
server.

[0081] In an embodiment, the apparatus carrying out embodiments of the
invention in the apparatus comprises at least one processor and at least
one memory including a computer program code, wherein the at least one
memory and the computer program code are configured, with the at least
one processor, to cause the apparatus to carry out the above-described
functionality for determining the transmission order, as described above
in connection with FIGS. 2 to 8. Accordingly, the at least one processor,
the memory, and the computer program code form processing means for
carrying out embodiments of the present invention in the apparatus.

[0082] FIG. 11 illustrates an embodiment of an apparatus comprising means
for carrying out the above-mentioned functionalities of the
above-described requesting device or the scanning device configured to
carry out an active scanning process involving the scanning request
messages and the scanning response messages. The apparatus may be a
wireless apparatus of an IEEE 802.11 network or another wireless network,
e.g. a STA. The apparatus may be a computer (PC), a laptop, a tablet
computer, a cellular phone, a palm computer, or any other apparatus
provided with radio communication capability. In another embodiment, the
apparatus is comprised in such a wireless apparatus, e.g. the apparatus
may comprise a physical circuitry, e.g. a chip, a processor, a micro
controller, or a combination of such circuitries in the wireless
apparatus.

[0083] The apparatus may comprise a communication controller circuitry 50
configured to control the communications in the wireless apparatus. The
communication controller circuitry 50 may comprise a control part 52
handling control signalling communication with respect to transmission,
reception, and extraction of control or management frames including the
scanning request messages and the scanning response messages, as
described above. The communication controller circuitry 50 may further
comprise a data part 56 that handles transmission and reception of
payload data during transmission opportunities of the wireless apparatus
(transmission) or transmission opportunities of other wireless
apparatuses (reception). The communication controller circuitry 50 may
further comprise an active scanning controller circuitry 58. The active
scanning controller circuitry 58 may be configured to handle the active
scanning procedure comprising the transmission of the scanning request
message comprising context information and the reception of the scanning
response messages. The active scanning controller circuitry 58 may be
configured to determine the context information included in the scanning
request message. The active scanning controller circuitry 58 may comprise
a transmission turn processor 54 configured to monitor for the
transmission turn indicators comprised in the acquired scanning response
messages and detect any response messages that has been missed according
to the embodiment of FIG. 9, for example.

[0084] The circuitries 52 to 58 of the communication controller circuitry
50 may be carried out by the one or more physical circuitries or
processors. In practice, the different circuitries may be realized by
different computer program modules. Depending on the specifications and
the design of the apparatus, the apparatus may comprise some of the
circuitries 52 to 58 or all of them.

[0085] The apparatus may further comprise a memory 60 to store computer
programs (software) configuring the apparatus to perform the
above-described functionalities of the scanning device. The memory 60 may
also store communication parameters and other information needed for the
wireless communications, e.g. contents and format of context information
to be added to the scanning response messages. The apparatus may further
comprise radio interface components 62 providing the apparatus with radio
communication capabilities within a service sets or between service sets.
The radio interface components 62 may comprise standard well-known
components such as amplifier, filter, frequency-converter, (de)modulator,
and encoder/decoder circuitries and one or more antennas. The apparatus
may further comprise a user interface enabling interaction with the user
of the communication device. The user interface may comprise a display, a
keypad or a keyboard, a loudspeaker, etc.

[0086] In an embodiment, the apparatus carrying out the embodiments of the
invention in the wireless apparatus comprises at least one processor and
at least one memory including a computer program code, wherein the at
least one memory and the computer program code are configured, with the
at least one processor, to cause the apparatus to carry out the
functionality of the scanning device described above in connection with
any one of the embodiments of FIGS. 2 to 9. Accordingly, the at least one
processor, the memory, and the computer program code form processing
means for carrying out embodiments of the present invention in the
apparatus functioning in the scanning device.

[0087] As used in this application, the term `circuitry` refers to all of
the following: (a) hardware-only circuit implementations such as
implementations in only analog and/or digital circuitry; (b) combinations
of circuits and software and/or firmware, such as (as applicable): (i) a
combination of processor(s) or processor cores; or (ii) portions of
processor(s)/software including digital signal processor(s), software,
and at least one memory that work together to cause an apparatus to
perform specific functions; and (c) circuits, such as a microprocessor(s)
or a portion of a microprocessor(s), that require software or firmware
for operation, even if the software or firmware is not physically
present.

[0088] This definition of `circuitry` applies to all uses of this term in
this application. As a further example, as used in this application, the
term "circuitry" would also cover an implementation of merely a processor
(or multiple processors) or portion of a processor, e.g. one core of a
multi-core processor, and its (or their) accompanying software and/or
firmware. The term "circuitry" would also cover, for example and if
applicable to the particular element, a baseband integrated circuit or
applications processor integrated circuit (ASIC) for the apparatus
according to an embodiment of the invention.

[0089] The processes or methods described in FIGS. 2 to 9 may also be
carried out in the form of a computer process defined by a computer
program. The computer program may be in source code form, object code
form, or in some intermediate form, and it may be stored in some sort of
carrier, which may be any entity or device capable of carrying the
program. Such carriers include transitory and/or non-transitory computer
media, e.g. a record medium, computer memory, read-only memory,
electrical carrier signal, telecommunications signal, and software
distribution package. Depending on the processing power needed, the
computer program may be executed in a single electronic digital
processing unit or it may be distributed amongst a number of processing
units.

[0090] The present invention is applicable to wireless communication
systems defined above but also to other suitable communication systems.
The protocols used, the specifications of communication systems, their
network elements and subscriber terminals, develop rapidly. Such
development may require extra changes to the described embodiments.
Therefore, all words and expressions should be interpreted broadly and
they are intended to illustrate, not to restrict, the embodiment. It will
be obvious to a person skilled in the art that, as technology advances,
the inventive concept can be implemented in various ways. The invention
and its embodiments are not limited to the examples described above but
may vary within the scope of the claims.

Patent applications by Eng Hwee Ong, Espoo FI

Patent applications by Gabor Bajko, Sunnyvale, CA US

Patent applications by Jarkko Kneckt, Espoo FI

Patent applications by Mika Kasslin, Espoo FI

Patent applications by NOKIA CORPORATION

Patent applications in class Control or access channel scanning

Patent applications in all subclasses Control or access channel scanning